Frequently Asked Questions

The contents of the Frequently Asked Questions are provided for informational purposes only and are not and should not be construed as medical advice, diagnosis, or treatment. Only a properly qualified physician can address specific questions regarding a patient’s health care needs. Individual inquiries about medical or healthcare issues should be addressed to appropriate healthcare professionals. Nothing contained in the Frequently Asked Questions should be used to replace or substitute for a patient's personal physician's advice.

General Testing FAQs -- answers to questions about screening and testing options.

The sample collected during invasive testing (CVS or amniocentesis) can be tested several different ways:

Chromosomal study (karyotype)*

Chromosomal microarray (aCGH)*

Single gene test or panel of genes*

*See glossary for descriptions of each test and discussions of the benefits and limitations of each test.

What is the difference between a screening test and a diagnostic test?

Everyone has a risk to have a child with a birth defect, single gene disorder and/or a chromosomal change. Screening tests are designed to determine if your risk for a specific condition or conditions is different (higher or lower) than your risk based on your age, pregnancy history and family history. Screening tests do not provide a definitive yes or no answer.

Once a risk has been identified, a diagnostic (invasive) test is used to provide a definitive yes or no answer for the tested condition (risk). We currently cannot test for all conditions, so no test can guarantee a healthy child.

Screening tests do not increase the risk for pregnancy complications, but may cause anxiety and may lead to invasive testing. Invasive testing may result in pregnancy complications and may cause anxiety.

Who should consider prenatal testing?

The American College of Obstetrics and Gynecology (ACOG) recommends that all women be offered prenatal screening and be given the option of invasive testing. If a woman considers her risk high enough to have invasive testing, chromosomal microarray testing (aCGH) should be considered for any pregnancy for which traditional karyotyping would be offered. Common reasons for performing karyotyping or aCGH include older maternal age, abnormal screening test indicating an increased risk for a chromosome abnormality, previous child or pregnancy with a known chromosome abnormality, abnormal ultrasound findings, and previous miscarriages or stillbirth.

What should I consider when comparing invasive and non-invasive testing?

Most women consider the level of risk and the type of condition for which they are at risk when deciding about prenatal testing. Is the condition for which you are at risk one that you are concerned about? Would you want to know if there was a problem?

Do you simply want to know if your risk is higher or lower than expected? Then non-invasive testing might be best.

Would you prefer a definitive yes or no answer for the condition(s) you are at risk for? Then an invasive (diagnostic) test might be best.

You can also start with a non-invasive screening test, and continue onto a definitive, invasive diagnostic test only if your risk on the screening test is elevated.

Diagnostic Testing FAQs

What is a chromosome test (karyotype) or cytogenetic testing?

Cytogenetic testing examines the number and structure of a person’s chromosomes through a microscope. Chromosomes are tightly bundled packages of DNA present in almost every cell in our bodies. Most people have 46 chromosomes. These chromosomes exist in two sets: we inherit one set of 23 chromosomes from our mother and one set of 23 chromosomes from our father. In this way, DNA is passed from parent to child and is the blueprint for the way our body forms and functions. Cytogenetic testing can detect extra or missing chromosomes or segments of chromosomes. In general changes visible under a microscope involve large segments of a chromosome or whole chromosomes. People with changes in their DNA or in the structure of their chromosomes may have birth defects, behavior issues, delay in development, or learning problems.

What is a chromosomal microarray test or array CGH?

Microarray-based comparative genomic hybridization (array CGH) is a type of cytogenetic test that uses DNA and provides much greater detail or higher resolution of parts of chromosomes that are extra or missing. The regions studied are known to be linked to birth defects, intellectual disability, or other medical or learning problems.

How is a chromosomal microarray test different from traditional cytogenetic testing?

Chromosomal microarray testing (aCGH) is a technology that evaluates chromosomes for extra or missing pieces smaller than can be detected by traditional cytogenetic testing, called karyotyping. Array CGH detects nearly all chromosome deletions and duplications that karyotyping detects but can also detect smaller extra or missing chromosome pieces that will be missed by karyotyping. These smaller alterations, often called "submicroscopic" alterations because they cannot be seen through the microscope, can cause major birth defects, developmental delay, autism, and genetic syndromes.

What do I need to know to decide between a chromosomal microarray test and a karyotype?

The risk to have a child with an extra or missing chromosome (Down syndrome, trisomy 13, trisomy 18, Turner syndrome, etc.) increases with maternal age, but can occur at any age. Both a karyotype and a chromosomal microarray test can detect most extra or missing chromosomes.

The risk for a missing or extra segment of a chromosome is not age related, and recent studies have found this risk to be about 1%. Some of these changes can be detected by a karyotype, but most are too small to be seen under a microscope. A chromosomal microarray test can detect most missing or extra chromosome segments.

Both tests will occasionally find a change that will require additional testing or may not be able to be interpreted. The risk for this type of “uncertain” result is greater with chromosomal microarray testing compared to a karyotype.

Neither test will detect all birth defects or genetic problems.

Under what circumstances is array CGH performed prenatally?

Although aCGH should be considered for any pregnancy for which routine karyotyping is offered, many doctors and genetic counselors routinely consider using array CGH technology for pregnancies in which an abnormality is seen by ultrasound evaluation (major birth defect like congenital heart disease, problems with growth, or cystic hygroma), or in pregnancies in which an abnormality in chromosome number or structure is detected by traditional karyotyping that could benefit from further studies using aCGH.

What are the risks with invasive testing (karyotype or microarray) testing?

Karyotyping and chromosomal microarray testing do not pose a health risk to the fetus or the mother. However, karyotyping and chromosomal microarray testing require a sample from the pregnancy, and the procedures performed to obtain the sample, such as amniocentesis or chorionic villus sampling (CVS), have a small risk of miscarriage associated with them. Your doctor or genetic counselor can talk to you about these risks and help you determine whether chromosome testing and array CGH are appropriate for your pregnancy. Both tests also have a risk that uncertain results will be found.

Are the risks different with chromosomal microarray testing?

The risk that an uncertain result will be found is higher with chromosomal microarray testing. This may result in additional testing, and the result may remain uncertain. The information that your doctor, geneticist or genetic counselor can provide and the natural history and expected outcome for some results from chromosomal microarray testing are not completely understood.

What are the benefits of chromosomal microarray (aCGH) testing?

Chromosomal microarray aCGH testing provides the highest resolution for detecting extra or missing parts of chromosomes available. A prenatal diagnosis of a specific condition can provide additional information that may enable your doctors to manage your pregnancy better and enable you and your doctors to know what to expect after delivery. Some parents choose to have aCGH testing because problems have arisen in their pregnancy, such as a non-reassuring maternal serum screen, abnormal ultrasound findings, or abnormal karyotype, and they want as much information as possible to make informed decisions. Other parents choose to have aCGH so they can plan and prepare for a child with anticipated medical or health issues. Still other parents choose aCGH testing to provide further reassurance that a chromosome problem does NOT exist in their pregnancy.

Can array CGH find all chromosome differences?

No, there are some chromosome differences that aCGH cannot detect, such as balanced rearrangements, changes in structure in areas of the chromosomes not evaluated by the array, change in a small percentage of the chromosomes, and having an entire extra set of 23 chromosomes.

What type of sample is needed?

aCGH is most commonly performed on cells that are obtained from a prenatal diagnosis procedure such as amniocentesis or CVS. Your doctor can help to determine which type of sample would be most appropriate to submit for analysis. Some laboratories also request parental blood samples.

Should I have a karyotype and array CGH test performed?

Recent studies have shown that aCGH can identify the same things as chromosome analysis (karyotype). When there is an indication of an increased risk for a balanced translocation or triploidy (a whole extra set of all chromosomes) both tests may be needed.

Why do some laboratories request blood samples from parents?

Occasionally, a difference in chromosome structure is detected in the fetal sample that has unclear clinical consequences. Not all changes in chromosome structure cause problems in a pregnancy or a person. Some changes run in families and do not cause any differences in health or learning. Other changes in chromosome structure cause birth defects or learning issues, the extent of which cannot be determined until after a child is born and begins to develop. When a change in the chromosomes is detected in a fetal sample, samples from parents are immediately evaluated to determine if one of the parents also has the change. If one parent has the change, the fetus is predicted to follow a course similar to that parent. This expedites the reporting of comprehensive results and alleviates anxiety.

What does a positive or abnormal array CGH result mean?

A positive or abnormal result means that a deletion or duplication in the chromosomes has been detected. The detected change has been seen in multiple children with problems in different families. Most of the currently available information is based on children diagnosed after birth because they have been diagnosed with problems. Your doctor or genetic counselor will provide current information about your specific results.

What does an uncertain or “variant of uncertain significance” result mean?

An uncertain result means that a segment of a chromosome is duplicated or missing. There have been very few or no reports of similar results in the medical literature and the meaning of this finding is “uncertain.” The genes in this segment have not been studied well enough to determine if having a missing or extra copy makes a difference (dosage sensitive). Some genes require two active copies (one from each parent). Other genes work well with only one copy. Some genes are okay with three copies. Uncertain results are often in regions of chromosomes where we do not have enough information to determine if two copies are necessary and only having one or having three copies would result in problems.

What does a negative or normal chromosomal microarray (aCGH) result mean?

A negative result means that the chromosomal microarray test did not detect a significant deletion or duplication in the chromosomes of the fetus. Most individuals have several very small deletions and duplications that are seen frequently and are felt to be normal. Many genetic conditions cannot be diagnosed by array CGH, especially those that are caused by differences in DNA that are too small for even array CGH to detect. Therefore a normal result cannot rule out all genetic problems. Your doctor will discuss the results with you.

I have additional questions about array CGH testing. Whom can I contact?

Patients, clinicians, and researchers registered with PrenatalDNAResource.org have access to experts in genetics and genetic testing. They can submit questions to our experts, as well as upload their genetic results for assistance with interpretation.

Also, your doctor, genetic counselor, or other genetics health care providers can talk with you more about the details of this testing. To find a genetic counselor, genetics clinic, or other genetics professionals in your area, please call your doctor, or use the “Find a Genetic Counselor” link at the National Society of Genetic Counselors website www.nsgc.org.

The contents of the Frequently Asked Questions are provided for informational purposes only and are not and should not be construed as medical advice, diagnosis, or treatment. Only a properly qualified physician can address specific questions regarding a patient’s health care needs. Individual inquiries about medical or healthcare issues should be addressed to appropriate healthcare professionals. Nothing contained in the Frequently Asked Questions should be used to replace or substitute for a patient's personal physician's advice.